Things you Always Thought You Knew

For quite a while now, I’ve made a small project of collecting things that everyone knows are true, but really aren’t true anyway. I’ve been working on this project on and off for quite some time, and come up with a few examples of such “common knowledge” so far. For example:

“It takes the police 2 minutes (or sixty seconds or some other amount of time) to trace a phone call.”

This has long been a staple of bad Hollywood thrillers–“Keep him talking! Keep him talking!”–but the fact is, tracing a phone call takes zero seconds. The call is traced before the phone has finished ringing. You don’t even need to answer it.

“There are three states of matter.”

Actually, there are six states of matter: Einstein-Bose condensate, superfluid, solid, liquid, gas, and plasma. Of the six, five occur naturally thorughout the universe (Einstein-Bose condensate occurs only in the lab); and four of those–solid, liquid, gas, and plasma–occur naturally on Earth.

“Someone who passes out on his feet will fall over backward.”

Also a staple of Hollywood. In reality, if you lose consciousness standing up, you fall over forward.

“There are three primary colors.”

The human visual system responds to photons with a wide range of diffeent wavelengths. Most people have three distinct receptors in their eyes, which are maxinally sensitive to a relatively narrow range of wavelengths; however, all three receptors do respond to all visible frequencies of light. (Some people have only two kinds of receptors; these people have red-green color blindness. A few people have four, and can distinguish colors most people can’t.)

Because all the receptors do respond to all frequencies of visible light, it is impossible to model certain colors based on any one set of primaries. For example, pure, 100% saturated yellow can not be modelled by any combination of red, green, and blue light. You can get yellow, but you can’t get pure yellow.

“Science says bumblebees can’t fly.”

Actually, science says bumblebees are aerodynamically unstable, which means they can’t glide. Many things that are aerodynamically unstable can fly–including bumblebees and Stealth fighters.

An aerodynamically unstable object can fly if it has an active stabilization system. In a bumblebee, that system is the animal’s sensory apparatus, brain, and muscles; in a Stealth fighter, it’s the plane’s gyroscope, onboard computer, hydraulics, and control surfaces.

In all such objects, if the active stabilization fails, the thing glides about as well as a rock.

“The Eskimoes have fifteen words for snow.”

This idea comes from a linguistic hypothesis called the Sapir-Whorf hypothesis, which postulates that a civilization will develop more words for concepts that are most important to it. In practice, it doesn’t quite work that way.

The Eskimoes have three words for “snow,” which translate roughly as “snow,” “sleet,” and “slush.” They also have a distinct word for snow on the ground versus snow in the air, but then, so does English; “blizzard” and “snowstorm,” as distinct from “snow.”

“The rubber tires on a car will protect the car’s occupants from lightning.”

This common misconception is downright dangerous. Yes, rubber is an insulator; however, rubber tires and rubber-soled shoes offer zero protection from high voltage. Air is also an insulator! Anything that can get through six miles of air is not going to stop for a few inches–or even a few feet–of rubber.

You are safe in a car, provided you do not touch any metallic object, because of the shape of the car, and its construction, not because of its tires. The electrical discharge will tend to travel around the car’s metallic shell, rather than passing through the metallic body and into the car. Rubber-soled shoes do not protect you from lightning (or other high-voltage discharges) one little bit.

“Water conducts electricity.”

Another common misconception about electricity. Pure water is an insulator. It does not conduct electricity. Water becomes a conductor only if there is a polar compound, such as salt, dissolved in it. It’s actually the salt (or whatever) that is carrying the electricity–not the water.